1. Field of the Invention
The present invention relates to a servo control of a hard disk drive, and in particular, to a technique for detecting a current position of a head by detecting an analog-to-digital conversion value detected at a single offset point.
2. Description of the Related Art
A hard disk drive, which is a disk driving recording apparatus, is widely used as an auxiliary memory device of a computer system because it can access a large amount of data at a high speed. A recording form broadly utilized in the hard disk drive has been based on constant-track-capacity. In this recording form, a spindle motor of the hard disk drive rotates at a constant velocity, and information capacity per track in inner and outer tracks of a magnetic disk is identical. However, the information recording density of the outer tracks is lower than that of the inner tracks. Therefore, the storage efficiency of the magnetic disk is degraded.
To overcome such a problem, a constant density recording form or a zone-bit recording form has been proposed. In the constant density recording form, all the tracks including the inner and outer tracks have the same information density in order to improve the information capacity of the magnetic disk, especially in a small-sized disk driving recording apparatus. Moreover, an information recording area on the magnetic disk is split into a plurality of zones so as to have constant recording density in the radial direction from the center of the magnetic disk. The number of data sectors is assigned differently to the tracks of each split zone. That is, the tracks of an outer zone have more data sectors in number than the tracks of an inner zone. The data sector designates a unit area that the hard disk drive accesses data on the magnetic disk and has the same size, 512 bytes for example, irrespective of its position on the magnetic disk. If an embedded sector servo system is used, one data sector may be split into two segments according to each area on the magnetic disk. The embedded sector servo system is one system for providing position information of a head in the disk driving recording apparatus. In the embedded sector servo system, each track is divided into a servo information area and a data information area which are alternatively provided in the direction of the circumference. The servo information area is an area for writing embedded servo information and provides a servo sector. The data information area is an area for writing actual data information is written and provides a data sector.
Since the above-mentioned constant density recording form causes all the tracks to have the substantially identical information density and can record more information per unit track than the conventional constant track capacity recording form, it has widely been used in the hard disk dive.
In a magnetic disk arrangement having the constant density recording form, two data sectors are disposed between servo sectors on a disk. The servo sectors for writing the servo information for the servo controller of the recording head consist of a preamble for adjusting synchronization with a system clock, a servo address mark for writing a reference pattern of servo timing generation, an index bit for providing information with respect to one rotation of the disk, a gray code area for writing track information and a plurality of servo burst areas for the on-track controller of the head.
Normally, burst signals A and B are written with a half value in adjacent tracks and used in detecting a position error signal of the head during track following. Burst signals C and D are written in even and odd tracks and used in discriminating the odd and even tracks respectively.
In the hard disk drive, the servo write pattern of each track is converted into a digital value from an analog value to obtain the position information of the head. To accurately obtain the position information of the head, the A/D conversion value must be processed so as to correspond to the position of the head.
Normally, a servo control means shifts the head to a particular offset point and repeatedly reads the burst signal written in the burst interval while the disk rotates a specified number of times. Thereafter, an average of the A/D conversion values of the detected burst signals is calculated and stored. The head is again shifted to another offset point and the above described steps are then repeated at the second point to obtain the A/D conversion value at that point. The position of the head is calculated utilizing the A/D conversion values at the two points. Since the A/D conversion values must be obtained at two points, the calibration process is delayed.
The following patents each disclose features in common with the present invention but do not teach or suggest the specifically recited technique for detecting the head position in a hard disk drive:
U.S. Pat. No.5,694,265 to Kosugi et al., entitled a Disk Apparatus for Detecting Position of Head by Reading Phase Servo Pattern, U.S. Pat. No. 5,523,900 to Kosugi et al., entitled a Head Position Detecting Method and Apparatus, U.S. Pat. No. 5,576,910 to Romano et al., entitled a Burst Comparison and Sequential Technique for Determining Servo Control in a Mass Storage Disk Device, U.S. Pat. No. 5,600,506 to Baum et al., entitled an Apparatus and Method for Determining the Position of a Transducer Relative to a Disk Surface in a Disk Drive System, U.S. Pat. No. 5,146,374 to Sakurai, entitled a Method and Apparatus for Determining Track Position of a Head on a Recording Medium, U.S. Pat. No.4,631,606 to Sugaya, entitled a System for Detecting the Position of a Read-write Head on a Disk Recording Medium Having Servo Sectors with Three or More Servo Patterns, U.S. Pat. No. 5,383,068 to Shimizu et al., entitled a Head Position Recognition Method, a Speed Calculation Method, and a Head Movement Speed Control Device, and U.S. Pat. No.5,105,318 to Tsuneta et al., entitled a Head Positioning Device for Use in Magnetic Disk Equipment.
It is therefore an object of the present invention to provide a head position detecting technique which can reduce a calibration execution time by detecting information needed to calculate a current position of a head at a single offset point.
According to one aspect of the present invention, a method for detecting a position of a head in a hard disk drive including at least one servo sector having a plurality of tracks in which servo burst signals are written includes the steps of: shifting the head to a track within which a crossing point of one of first and second servo burst signals written up and down with respect to the center of the track and a third burst signal written symmetrically with respect to the center of the track is situated; detecting an analog-to-digital conversion value at the crossing point; and calculating the position of the head by the following equation:   Position  =                    (                              burst            ⁢                          xe2x80x83                        ⁢            A                    -                      burst            ⁢                          xe2x80x83                        ⁢            B                          )            xc3x97              (                              T            max                    /          2                )                            (                              burst            ⁢                          xe2x80x83                        ⁢            A                    +                      burst            ⁢                          xe2x80x83                        ⁢            B                          )            -              2        xc3x97                  P2          xe2x80x2                    
where burst A and burst B are analog-to-digital conversion values of the first and second burst signals, Tmax is a constant value when one track is designated as the basis of position information, P2xe2x80x2 is an analog-to-digital conversion value at the crossing point of the crossing burst signals.